This invention relates to power actuators for vehicle closure panels generally, and specifically to a non binding toothed rack and channel track type of drive assembly for a power actuator.
More and more vehicles are incorporating power actuated closure panels, such as doors, hoods, trunk lids and rear liftgates. One such device particularly useful for a rear liftgate of the type found on minivans and SUVs is a stationary electric motor that turns a toothed wheel to slide an elongated toothed rack up and down inside a channel track. A link between the toothed rack and the liftgate pushes it up and open or swings in down and closed. Two such devices, one on each side, may be needed for large and heavy rear liftgates. Typically, the link between the power actuator and the rear liftgate is a rod that is attached at an upper end to the liftgate by a ball joint, and attached directly to the toothed rack by another ball joint at the lower end. The rod is subjected to shifting, twisting reactive loads as it moves up and down, and these are translated directly to the moving toothed rack sliding within the channel track. The non axial reactive loads tend to cause the rack to twist and bind within the channel track.
The subject invention provides an improved connection between the toothed rack and the lift rod that allows the toothed rack to slide within the channel track as it moves the lift rod up and down, but which prevents the lift rod from reacting on the toothed rack to bind it within the track.
In the embodiment disclosed, the toothed rack is thin enough and narrow enough to slide within the interior of the channel track with a significant clearance all the way around. A rigid yoke has a pair of side walls that straddle a notch in the upper surface of the rack, fitting closely into the axially spaced ends of the notch but spaced apart sufficiently to significantly clear the sides of the rack other than at the ends of the notch. A ball stud on the top of the yoke is pivotally joined to the lower end of the lift rod. An outer shoe of suitable bearing material, solid, but not as rigid as the yoke, surrounds the yoke, and fits closely to both the outer surface of the yoke and to the inner surface of the channel track. When the rack-yoke-shoe subassembly is installed in the channel track, the close fit of the shoe to both the inside of the track and the outside of the yoke maintains the yoke""s clearance from the rack.
In operation, the yoke-shoe assembly slides closely back and forth within the track as the toothed wheel shifts the rack, with axial loads being efficiently transferred between the rack and yoke by the close fit to the ends of the rack notch. The all round clearance maintained by the shoe at all other points between the rack and yoke prevents non axial twisting loads from being transferred back from the yoke to the rack, however, so that the rack does not bind within the channel track. Twisting loads are instead transferred from the yoke, through the surrounding shoe, to the close fitting channel track.